This is a simple script using the Twilio PHP Helper library to retrieve Recordings within a certain date range and then delete them.

delete-recordings.php

<?php
// This assumes you have the Twilio PHP Helper library
require 'Services/Twilio.php';

// This is a file with my Account Sid and AuthToken
include 'credentials.php';

$client = new Services_Twilio($accountsid, $authtoken);

/*
 * For the getIterator array, these are valid options: 
 *   "DateCreated>" or "DateCreated<"
 */
foreach ($client->account->recordings->getIterator(0, 50, array('DateCreated>' => '2011-07-05 08:00:00', 'DateCreated<' => '2011-08-01')) as $recording) {

    echo $recording->sid." -- ". $recording->date_created . "\n";
    $client->account->recordings->delete($recording->sid);
}